The present invention relates to an image pickup system capable of picking up a wide range such as an omnidirectional or full-circumferential image.
As is generally known, a variety of cameras for simultaneously shooting omnidirectional or full-circumferential images, which comprise a multiplicity of video cameras contained in a casing, have been developed.
As one of the methods for the simultaneous image pickup, for example, a method has been proposed in which the parallax which may be generated among a plurality of cameras is dissolved by ensuring that image pickup view points virtually coincide with each other by use of mirrors arranged in the form of a polygonal pyramid (see U.S. Pat. No. 6,115,176).
A general constitution of one example of the above-mentioned image pickup system using the mirrors arranged in the form of a polygonal pyramid is shown in FIG. 6. The image pickup system comprises eight plane mirrors 44 arranged in a polygonal pyramid, in this case, an octagonal pyramid, and cameras 41 arranged opposite the plane mirrors 44 in one-to-one correspondence respectively. In FIG. 6, two plane mirrors 44 and two cameras 41 disposed on a vertical plane containing the centerline of the image pickup system are shown. Each camera 41 comprises a lens 42 and an image pickup device 43, and the camera 41 is assembled by attaching the lens 42 to a camera main body (not shown) in which the image pickup device 43 and other component parts are contained.
In the image pickup system, angle-of-view end rays 46A passing through the uppermost portion of the angle of view, angle-of-view end rays 46B passing through the lowermost portion of the angle of view, and a ray passing along the optical axis 47 of the lens 42 and reflected by the mirror 44, are incident on the lens 42, and are focused to form an image on the image pickup device 43.
In the plurality of cameras 41, the virtual view centers 45 generated by the plane mirrors 44 are caused to substantially coincide with each other, whereby parallax can be restrained. As a result, by splicing the images picked up by the plurality of cameras 41, wide-range images such as an omnidirectional or full-circumferential image can be obtained.
In the case of FIG. 6, the angle of incidence of the ray passing along the lens optical axis 47 on the plane mirror 44 is 45 degrees. Therefore, the ray passing along the lens optical axis 47 is horizontally incident on the plane mirror 44, is reflected by the plane mirror 44, and is vertically incident on the lens 42.
In the image pickup system shown in FIG. 6, the distance between the angle-of-view end rays 46A passing through the lowermost portion of the angle of view and a tip corner of the lens 42 is CL. So that the tip of the lens 42 is not mirrored, i.e., to pick up an image free of xe2x80x9ceclipsexe2x80x9d (shading), it is necessary that CL greater than 0.
As shown in FIG. 6, the factors dominantly determining the size of the image pickup system are the height HL from the upper end of the mirror 44 to the lower end of the camera 41 (in FIG. 6, to the image pickup device 43), and the extent LL between the upper end portion of the octagonal pyramid form mirrors 44. Then, in order to reduce the image pickup system in size, it is required to reduce the height HL and the extent LL.
In order to reduce the height HL and the extent LL, it suffices to set the cameras 41 (the lenses 42 and the image pickup devices 43) closer to the plane mirrors, as shown in FIG. 7. As a result, the plane mirrors 44S can be made to be smaller than the plane mirrors 44 in FIG. 6, and the height HS from the upper end of the mirror 44S to the lower end of the camera 41 and the extent LS of the upper end portion of the octagonal pyramid form mirror 44S satisfy HS less than HL and LS less than LL.
In the case of FIG. 7, however, the distance between the angle-of-view end rays passing through the lowermost portion of the angle of view and the tip corner of the lens 42 is xe2x80x9cnegativexe2x80x9d, and xe2x80x9ceclipsexe2x80x9d (shading) occurs, which is inconvenient for image pickup. Therefore, it is necessary that the distance C (best shown in FIG. 8) between the angle-of-view end rays passing through the lowermost portion of the angle of view and the tip corner of the lens 42 be positive and as small as possible. In this instance, the diameter D of the tip end of the lens 42 of the camera 41 constitutes a restriction on the reduction of the size of the image pickup system.
From the foregoing, the camera 41 cannot be set closer to the plane mirror than the position where the distance C=0. Besides, in the case where the size (particularly the width) of the camera main body 41A in which the image pickup device 43 and the like are contained is much larger as compared with the lens 42, as indicated by broken line in FIG. 6, the camera main bodies 41A of the plurality of cameras 41 will interfere with each other as the cameras 41 are brought closer to the plane mirrors. For example, where each camera is composed by use of three CCD image pickup devices, the camera main body is considerably large.
Due to these restrictions, it has been difficult to achieve a further reduction in the size of the image pickup system. In addition, in the constitution of the image pickup system shown in FIG. 6, the plane mirror 44 and the optical axis 47 of the lens 42 of the camera 41 are in the positional relationship of the incidence angle of 45 degrees, and this positional relationship determines the size of the plane mirrors 44; as a result, the size of the polygonal pyramid form mirror and the overall size of the image pickup system become large.
Particularly, the factors dominantly determining the size of the image pickup device are the height HL from the upper end of the plane mirror 44 to the lower end of the camera 41 and the extent LL of the upper end portion of the pyramid form mirror 44. Furthermore, the values of the height HL and the extent LL are influenced also by the distance C (CL in FIG. 6) between the angle-of-view end rays passing through the lowermost portion of the angle of view and the tip corner of the lens 42, and, therefore, it is necessary to appropriately set the distance C.
However, the virtual view centers 45 of the plurality of cameras 41 can be caused to substantially coincide with each other, independently from the value of the distance C, so that the distance C can take an arbitrary value. Hitherto, the distance C has not been set to an appropriate value, and, accordingly, the image pickup device has been large in overall size.
In order to solve the above-mentioned problems, it is an object of the present invention to provide an image pickup system having a smaller size, by reducing the sizes of the mirrors and the image pickup device as a whole.
In accordance with one aspect of the present invention, there is provided an image pickup system comprising a plurality of plane mirrors arranged in the form of a polygonal pyramid, and a plurality of cameras disposed opposite the mirrors respectively, wherein the angle of incidence of the ray passing along the optical axis of a lens of each camera on the plane mirror is less than 45 degrees.
According to the above constitution of the image pickup system according to the present invention, since the angle of incidence of the ray passing along the optical axis of the lens of the camera on the plane mirror is less than 45 degrees, the height from the upper end of the plane mirror to the lower end of the camera can be reduced, and the area of the base surface of the polygonal pyramid constituted of the plane mirrors can be reduced. As a result, it is possible to reduce the overall size of the image pickup system.
In accordance with another aspect of the present invention, there is provided an image pickup system comprising a plurality of plane mirrors arranged in the form of a polygonal pyramid and a plurality of cameras disposed opposite the plane mirrors respectively, wherein the relationships of D/A less than 4 and f/D greater than 0.15 are fulfilled, where D is the diameter of the tip portion of a lens of the camera, f is the focal length of the lens, and A is the diagonal length of an image pickup device of the camera.
According to the above constitution of the image pickup system according to the present invention, since the relationships of D/A less than 4 and f/D greater than 5 are fulfilled, where D is the diameter of the tip portion of the lens of the camera, f is the focal length of the lens, and A is the diagonal length of the image pickup device of the camera, it is possible to reduce the diameter D of the tip portion of the lens under the condition where the diagonal length A of the image pickup device and the focal length f of the lens are fixed, and thereby reducing the size of the image pickup system.
In accordance with a further aspect of the present invention, there is provided an image pickup system comprising a plurality of plane mirrors arranged in the form of a polygonal pyramid, and a plurality of cameras disposed opposite the plane mirrors respectively, wherein the relationship of 0 less than C less than 2A is fulfilled, where C is the distance from a tip corner of a lens of the mirror to an image pickup angle-of-view end ray nearest thereto, and A is the diagonal length of an image pickup device of the camera.
According to the above constitution of the image pickup system according to the present invention, since the relationship of 0 less than C less than 2A is fulfilled, where C is the distance from the tip corner of the lens of the camera to the image pickup angle-of-view end ray nearest thereto, and A is the diagonal length of the image pickup device of the camera, it is possible to reduce the distance C from the tip corner of the lens of the camera to the image pickup angle-of-view end ray nearest thereto under the condition where the diagonal length A of the image pickup device is fixed, and thereby reducing the size of the image pickup system.